Salvatore Sirigu's error shortly before the interval proved costly for Laurent Blanc's men, who had led through Edinson Cavani, as they stayed second and a point behind Marseille.
PSG had won the previous nine matches in all competitions and, after a rocky start, were ahead 29 minutes in against struggling Lille as Cavani finished Ezequiel Lavezzi's dangerous cross from the left.
The champions were unable to take that lead into the break, however, as Sirigu failed to deal with David Rozehnal's header - clumsily fumbling the ball into his own net.
With first place at stake following Marseille's draw with Lorient on Tuesday, Blanc's side could not find a winner in the absence of rested striker Zlatan Ibrahimovic.
In fact, Lille - whose winless run now stands at 11 games in all competitions - had opportunities to gain a surprise victory as they held firm to frustrate Blanc and pick up a deserved point.
Despite their woeful recent form, the hosts had three opportunities to take the lead in the very first minute of the match.
Sirigu's terrific double save denied Divock Origi and then Nolan Roux before the ball broke loose to Florent Balmont, who could only hit the post.
Origi and Roux continued to threaten PSG's backline, which included Gregory van der Wiel and Maxwell at the expense of Lucas Digne and Serge Aurier, although Lucas Moura's low drive tested Vincent Enyeama at the other end inside the opening 10 minutes.
Cavani then wasted a gilt-edged opportunity as he sidefooted Maxwell's cutback wide from inside the area, with Lille's bright start fading before the half-hour mark.
Conversely, PSG grew into the game and duly took the lead through Cavani.
After a purposeful burst infield from Lucas, the Brazilian played in Lavezzi to cross with Cavani applying the finish for his seventh league goal of the campaign.
While Balmont's withdrawal due to an apparent foot injury looked set to cap a disappointing half for Girard's men, a slightly fortuitous equaliser brightened the mood at the Stade Pierre Mauroy.
Rozehnal's glanced header was fumbled by Sirigu, with neither the goalkeeper nor Javier Pastore on the post able to keep it out.
Lille started the second half on top - Origi and Simon Kjaer both testing Sirigu - before a jinking run from Lucas allowed the PSG man strike the underside of Enyeama's crossbar.
Blanc then gave Marco Verratti his first taste of action since November's win over Marseille off the bench following an adductor injury, but the Italian could not lift a below-par PSG and they were forced to settle for a point.